Water softener units utilizing ion exchange resin particles must be regenerated periodically with a brine solution to restore the water hardness removing ability of such particles. When iron is present in the water being treated it is advantageous to include weak acids, such as citric acid, in the regeneration solution. A supply of such acid is stored in a separate container and a metered dose is dispensed into the brine tank during each regeneration cycle of the water softener. A variety of types of acid dispensers have been used in the past, and each had disadvantages. For example, the amount of acid dispensed might vary over a long period of time as the parts of the dispenser became worn or lost their elasticity, or all of the acid in the storage container might be dispensed in a single cycle if the dispenser failed to shut off properly.